Two doses of Pfizer or AstraZeneca vaccines 'effective against Delta variant'

Vaccines are highly effective against the Delta strain, which is now the dominant variant worldwide, study shows

A health worker administers the AstraZeneca-Oxford vaccine at a centre set up in the Fazl Mosque in London. AFP

Two doses of Pfizer or AstraZeneca's vaccine are nearly as effective against the Delta coronavirus variant as they are against the previously dominant Alpha strain, a study published on Wednesday showed.

Officials say vaccines are highly effective against the Delta variant, which is now the dominant variant worldwide, although the study repeated that one shot of the vaccines was not enough for high protection.

The study, in the New England Journal of Medicine, confirms findings given by Public Health England in May about the efficacy of Covid-19 vaccines made by Pfizer-BioNTech and Oxford-AstraZeneca, based on real-world data.

The study found two doses of Pfizer's shot was 88 per cent effective at preventing symptomatic disease from the Delta strain, compared to 93.7 per cent against the Alpha, about the same as previously reported.

Two shots of AstraZeneca's vaccine were 67 per cent effective against the Delta variant, up from 60 per cent originally reported, and 74.5 per cent effective against the Alpha variant, compared to an original 66 per cent.

"Only modest differences in vaccine effectiveness were noted with the Delta variant as compared with the Alpha variant after the receipt of two vaccine doses," Public Health England researchers wrote in the study.

Data from Israel has estimated lower effectiveness of Pfizer's shot against symptomatic disease, although protection against severe disease remains high.

Public Health England previously said a first dose of either vaccine was about 33 per cent effective against symptomatic disease from the Delta variant.

The full study published on Wednesday found that one dose of Pfizer's shot was 36 per cent effective, and one dose of AstraZeneca's about 30 per cent.

"Our finding of reduced effectiveness after the first dose would support efforts to maximise vaccine uptake with two doses among vulnerable groups in the context of circulation of the Delta variant," the authors said.